This disclosure relates to the field of surgical repair of phalangeal deformities such as hammer toe, by arthrodesis. An intramedullary anchor structure has an asymmetrically tapered barbed point enabling the point to be inserted over a range of starting angles relative to a longitudinal bore in a phalanx during a surgical procedure. The asymmetric point is configured to align the anchor structure to the bore when fully inserted, and fix the anchor structure against retraction from the bore.
A hammer toe or contracted toe is a deformity of the proximal interphalangeal joint of the second, third, or fourth toe, typically arising if the proximal phalanx at the proximal interphalangeal joint is habitually oriented upward while the more distal phalanges are curved over and downward, for example due to tight or poorly fit shoes. The muscles and joints of the toe assume a permanent contracted hammer shape. Wear points can develop calluses or corns, especially on the superior side of the proximal joint.
A hammer toe condition can be corrected by podiatric surgery. Traditional hammer toe arthrodesis (fusing) has the object of resetting and fusing the anatomical alignment of the phalanges at the proximal interphalangeal joint. A percutaneous intramedullary support known as a Kirschner-wire or K-wire, comprising a length of stiff metal wire, is embedded by insertion lengthwise through the distal phalanx, and lengthwise through the distal and proximal interphalangeal joints. A protruding end of the K-wire remains accessible at the distal end of the toe. The K-wire immobilizes the phalanges in a more nearly co-linear horizontal configuration. After a period of healing sufficient for the bones to fuse across the proximal interphalangeal joint, for example six weeks, the K-wire is removed, i.e., retracted lengthwise from the distal end of the toe.
K-wire arthodesis has some drawbacks including the need for the K-wire to traverse and potentially interfere unnecessarily with the distal interphalangeal joint. There are potential issues with infection due to the protruding wire. An alternative arthrodesis technique is to incise and dislocate the toe at the proximal interphalangeal joint and to insert and permanently embed an intramedullary support into both of the phalanges at the proximal interphalangeal joint, without insertion from the end of the toe. The intramedullary support, such as a short length of K-wire or another elongated supporting structure, is inserted into longitudinal bores extending proximally into the third phalanx and distally into the second phalanx. That is, the support is inserted oppositely endwise into both of the two phalanges that abut at the proximal phalangeal joint.
It is desirable for the elongated intramedullary support to extend well into both phalanges for good structural support. The intramedullary support should bottom out substantially in the bores formed in both phalanges when the phalanges are in abutment, to reduce the opportunity for displacement of the bones away from abutment where the bones are to be fused. After forming the bores, it is necessary to insert the intramedullary support endwise into the bore of the one of the two phalanges, and then relatively to displace the phalanges longitudinally away from one another by a sufficient distance to clear the protruding length of the intramedullary support.
For example, an intramedullary support might be inserted first in the proximal phalanx of the proximal interphalangeal joint, proximally up to the point of bottoming out in the bore. The length of the intramedullary support that protrudes from the proximal phalanx is equal to the length of the bore in the next distal phalanx so the support will bottom out there as well. The protruding length could be, for example, 75% of the length of the next distal phalanx, namely the length of the bore therein. In order to complete the assembly, the phalanges are pulled longitudinally apart, by at least the protruding length of the intramedullary support. While holding the phalanges in co-linear alignment, the bore in the distal phalanx is aligned with the protruding end of the intramedullary support, and the distal phalanx then is pushed proximally along the intramedullary support to abut against the proximal phalanx.
A short length of K-wire can be used as a permanent intramedullary support, bridging across the proximal interphalangeal joint but not protruding distally from the end of the toe. There are also intramedullary hammer toe implants with other structures available. One object of the intramedullary support is to immobilize the phalanges in abutment at the joint, namely to prevent relative displacement of the phalanges, which would delay or prevent them from fusing. One-way intramedullary structures are possible, for example, with barbed ends. An oppositely barbed intramedullary support is disclosed, for example, in US 2011/0257652-Roman. Embodiments with one end threaded and the other end barbed are disclosed in US 2013/0131822-Lewis. These disclosures are incorporated herein by reference. At least one barbed end is advantageous because when the bones at the joint are pushed onto a barbed intramedullary, the points or flukes of the barbed ends engage in the bone tissue, preventing retraction, and to some extent, preventing relative rotation of the bones. However regardless of engaging structure, in order to insert the intramedullary into the second of the two bones at the joint, the bones need to be separated longitudinally by the protruding length of the intramedullary, namely the length that is to be inserted into the second of the two bones.
The object is to re-position the phalanges substantially co-linearly at the joint, both phalanges being horizontal along their longitudinal extensions or having a slight plantar flex, e.g., 10°, and to fuse the phalanges across the joint in that orientation. The surgical procedure includes an incision on the superior side of the joint. The joint is dislocated for access through the incision to the abutting ends of the phalanges. The ends of one or both of the phalanges can be resected. For example, the distal phalange can be shortened by trimming its proximal end. Opposite longitudinal bores are formed in each of the abutting phalanges at the joint, e.g., drilled and broached. An intramedullary support is inserted into the bore in one of the phalanges, particularly the proximal phalanx. The support is sized to protrude when fully inserted into the proximal phalanx, by substantially the same distance it will be inserted into the next distal phalanx, both end bottoming out or coming close to bottoming out in their respective bores. The distal phalange is pulled out over the protruding end of the intramedullary support, and pushed onto the protruding end. The joint capsule is sutured over the support and the incision is sutured closed. The phalanges heal with the interphalangeal joint fused.
The dimensions of the phalanges, the bores for receiving the intramedullary support and the intramedullary support itself are small and a challenge to manipulate. What is needed is an improved structure for the intramedullary support and improved techniques placing the support, that are less reliant on separating and aligning the bores in the abutting phalanges to the ends of an intramedullary support.